In early 2015, Alexander Payne found himself uncharacteristically at loose ends. The director of “Sideways” and “Election” was at an impasse with the film he was making, “Downsizing.”

While studying at Stanford, Payne enjoyed visiting San Francisco, and he thought moving to the city for two months might rejuvenate him. He took an apartment on the top of Russian Hill and became a regular at a neighborhood yoga studio.

Two days a week, he interned as a prep cook at Chez Panisse in Berkeley. “Mostly I swept floors,” Payne recalled with a laugh.

The break worked magic, both personally and professionally. In October 2015, he married Maria Kontos, a Greek philologist he met while touring Aigio, a town in west Greece where his family emigrated from.

Payne returned to “Downsizing” with new vigor and completed the movie, his most multilayered story to date. From the trailer, it appears to be a comedy about humans who can be shrunk to the size of a finger and thereby afford luxuries such as mansions denied their normal-size counterparts. In the preview, Matt Damon wakes up from the miniaturizing procedure and checks under the sheets for reassurance that his male essentials are still intact.

But Payne and Jim Taylor, his frequent co-writer, aim for far more than laughs. Although never sounding like a polemic, “Downsizing” takes on such timely issues as the diminution of the planet’s resources, climate change and the rights of refugees. The film, which was 10 years in the works, is at times remarkably prescient, depicting Mexicans living behind a wall, among other scenes.

So many big ideas could have been more broadly explored in a television miniseries. “But I like movies,” said Payne, who has made seven of them over 21 years.

With all this ground to cover, “You have to make a decision about what to pay attention to and what to ignore,” he said. “You can’t go nuts showing a lot of realistic aspects of shrinking people.”

While he consulted experts on the physics of shrinking humans, most of this information does not appear onscreen. “You can survive a fall from a relatively higher height,” the director said, rattling off what he learned. “If you stretched Popsicle sticks to your arms, you could fly a little bit. The quality of your voice would change. We tried tweaking (the actors’) voices to make them tinnier, but not so much that it grew into a distraction.”

Payne greeted extensive digital effects as “a new bag of tricks.” At the same time, he wanted them to be “so believable as to be banal. I didn’t want to get hung up on them.”

His most crucial decision was casting the lead role of an average guy seduced by the luxuries that would come his way. Payne’s template was James Stewart’s everyman in “It’s a Wonderful Life.”

In his mind, the only contemporary actor to fit the bill who also would be the right age was Matt Damon. “Matt looks really normal. He looks like someone you might have gone to high school with, a good guy who played ball. If he is actually a movie star inside, he does a very good impression of being a nice guy.”

Comparing Damon to his good friend Ben Affleck, Payne said, “I don’t think Ben looks so much like an average person. He looks like a movie star.”

Working together for the first time, Damon and Payne gained a mutual admiration. “Matt was very helpful on the set. He was a font of ideas. He has learned directing from all the great directors he’s worked with,” Payne said.

Meanwhile, Damon is quoted in “Variety” saying his job is made “so much easier with a director like Alex who’s so sure-handed.”

Payne laughs when reminded of his star’s quote. “First of all, I don’t always know what I’m doing. Like with any job, there are parts you really know what the hell you are doing and other times you don’t. But it helps when you have written the script.”

His screenplays for “Sideways” and “The Descendants” have won Oscars. (He is a three-time nominee for best director.)

His first nomination for best screenplay came with “Election,” which was only his second film. At a gas station when the news came, “I was so excited I filled up my car with premium and my car didn’t take premium,” he recalled.

But Payne, who was cited by the Hollywood Reporter for having “never made a bad movie,” isn’t one of those directors who insists on writing every script himself. “Nebraska” was written by Bob Nelson.

“I write out of desperation, never having read a script other than ‘Nebraska’ that I wanted to direct. I have been very picky about the screenplay. On the one hand, I wish I were like the old studio directors who (working with the studio’s screenwriters) would do three films a year. On the other hand, I want to make a film when I have something to say. The idea has to sustain you.

“Right now, I have maybe five film ideas, but I have not put a spade in the earth. If any of your readers have a good idea, get ahold of me. Oh God, yes, please save me.”

Ruthe Stein is the San Francisco Chronicle’s senior movie correspondent.